Thermostatic switch assembled with a single fastener



Sept. 30, n. J. SCHMITT 3,470,518l

THERMOSTATIC SWITCH ASSEMBLED WITH A SINGLE FASTENER Filed March '7, 1967 INVENTOR.

00A/,4.40 J CHM/77' United States Patent O 3,470,518 THERMOSTATIC SWITCH ASSEMBLED WITH A SINGLE FASTENER Donald I. Schmitt, Mansfield, Ohio, assignor, by mesne assignments, to Therm-G-Disc, Incorporated, a corporation of Ohio (1968) Filed Mar. 7, 1967, Ser. No. 621,239 Int. Cl. H0111 37/46 U.S. Cl. :B7-3% 16 Claims ABSTRACT F THE DISCLOSURE A thermostat operated by a bimetallic disc constructed to minimize manufacturing costs, 'and to provide accuracy and reliability of operation. A single rivet mounts the two switch contacts and an insulating member. The insulating member separates the two contacts and closes the switch body. Accuracy of contact location is provided by engagement between body Walls and contact members remote from the rivet. A bimetallic snap-disc switch actuator is mounted on the body by a cup-shaped cover. The cover is secured to the body by radially deforming the cover Wall.

Background of invention This invention relates generally to thermostats and more particularly to a novel and improved thermostat actuated by a snap-disc element constructed and arranged to -minimize manufacturing costs and improve operating accuracy and reliability.

Thermostatic switches are widely used in the controls of furnaces, heaters and appliances. Since such devices are used in great numbers it is essential that the manufacturing cost of each device be reduced as low as possible. However, such cost reductions must not be made at the expense of operating accuracy and reliability, since the proper functioning of the associated controls, and in some cases the safety of the user, depends on proper operation of the thermostat.

Generally, thermostatic switches include a body provided vvith a switch cavity, a pair of electrical contact members, one xed and the other movable, and a temperature sensing mechanism arranged to move the movable contact member into and out of contact with the fixed contact member in response to predetermined temperature conditions. Means are normally provided to mount the contact members and the sensing device on the body and to close and seal the mechanism to prevent physical damage to the elements and the entry of damaging contaminants. `Operating accuracy requires that the various parts be precisely located relative to the body, since any movement causing changes in the alignment of the parts can result in changes in the operating characteristics.

There are two principal categories of cost involved in the manufacture of thermostatic switches. One is the cost of manufacturing the component parts and the other is the cost of assembling the parts into the complete device. In a thermostat incorporating the present invention both of these categories of cost are reduced while still providing operating accuracy and reliability.

Summary of invention In the illustrated embodiments of this invention a single rivet is used to mount both switch contacts and the switch cavity cover. The switch cavity cover also serves to insulate the two contacts from each other. By combining the function of certain of the partsthe total number of parts is reduced. Further, the use of a single rivet to mount the two contacts and the switch cover reduces the 3,470,518 Patented Sept. 30, 1969 number of operations necessary for the assembly of the complete device. The illustrated embodiments of this invention require only eight component parts and two main assembly operations.

The body and the contacts are provided with opposed surfaces at locations spaced from the rivet which abut with the contacts and cooperate with the rivet to provide precise location of the contacts. With this structure the operating accuracy is maintained even when the connecting terminals are subjected to loads which would otherwise tend to change the orientation of the contacts. The fixed contact is deflected from its unstressed condition during assembly by engagement with an abutting locating surface on the body adjacent to the contact itself. 'Ibis insures that the -tixed contact is precisely positioned without requiring extremely close tolerances in the manufacture of the fixed contact. The snap-disc is mounted on the body by a cover member arranged for easy assembly and accurate positioning of the disc.

Objects of invention It is an important object of this invention to provide a novel and improved thermostat wherein the parts are constructed and arranged to minimize the cost of manufacturing the parts and the cost of assembling the complete device.

It is another important object of this invention to provide a novel and improved thermostat according to the preceding object wherein all of the switch parts and the switch cover are secured in position by a single fastener.

It is still another object of this invention to provide a novel and improved thermostat according to the last preceding object wherein opposed surfaces are provided on the contact members of the switch and the thermostat body which cooperate with the single fastener to precisely locate the contact members.

It is another important object of this invention to provide a novel and improved thermostat according to any of the preceding objects wherein a snap-disc temperature sensing element is provided to operate a switch and wherein a cover element which operates to mount the bimetallic element on the thermostat body is secured to the body by simplied means.

Further objects and advantages will appear from the following description and drawings wherein FIGURE 1 is a plan view of a rst embodiment of a thermostatic switch incorporating this invention;

FIGURE 2 is a side elevation of the thermostat i1- lustrated in FIGURE l;

FIGURE 3 is an enlarged, cross-section, taken along 3 3 of FIGURE l, illustrating the structural detail of the assembled thermostat;

FIGURE 4 is a fragmentary cross-section, taken along 4 4 OfQFIGURE 3;

FIGURE 4a is a fragmentary, perspective view of a modified structure for precisely positioning the fixed contact member;

FIGURE 5 is -an enlarged fragmentary section taken along 5 5 of FIGURE 1, illustrating the structural detail of one arrangement for mounting the cup-shaped disc cover;

FIGURE 6 is a plan View of a modified form of thermostat incorporating this invention having a modified arrangement for mounting the disc cover; Iand FIGURE 7 is an enlarged fragmentary section, taken along 7 7 of FIGURE 6.

Referring Ato FIGURES 1 through 5, the tirst embodiment of this invention includes a molded body 10 formed of any suitable dielectric material. For thermostats intended to operate at relatively high temperatures the body is normally formed of a ceramic material. For lower temperature thenmostats the body may be formed of plastic, such as Bakelite or the like. The switch mechanism includes a stationary contact 11 and a movable contact 12. The stationary contact 11 is formed of a relatively heavy gauge strip of metal bent to the shape illustrated. It includes a mounting portion 13, a terminal portion 14 and a switch portion 16. A contact button 17 is mounted on the end of the switch portion 16.

The movable contact 12 is formed of two parts welded together. A substantially rigid part 18 is preferably formed of relatively thick metal cut and shaped to provide a mounting portion 19 and a terminal portion 21. The other part 22 of the movable contact 12 is formed of relatively thin spring stock spot welded at 23' to the rigid part 18. A second contact button 24, mounted on the end of the spring part 22, moves into and out of electrical contact with the contact button 17 when the switch is operated.

An insulating member 26 extends between the two contacts 11 and 12 to insulate them from each other and also extends lengthwise of the body to close the switching cavity 27. A single rivet 28 extends through the mounting portion 19 of the movable contact 12, the insulating element 26, and the mounting portion 13 of the stationary contact 11. This single rivet is the only fastener required for the mounting of the two contacts 'and the insulating member 26. The flexible part 22 of the movable contact 12 has a mounting portion 29 extending along the upper side of the insulating member 26 in engagement with the rigid part 18, and a contact portion 30. The contact portion 30 includes a depending portion 31 which extends down through an aperture 32 in the insulating element 26 to a portion 33 on which the contact button 24 is mounted.

The rigid part 18 of .the movable contact element 12 is formed with an extension 34 which projects along the insulating element 26 past the aperture 32 to close the aperture when the switch is assembled. This projection 34 is provided with opposed edges 36 and 37 which closely lit opposed surfaces E18-and 39, respectively, on the body 10 and cooperate with the rivet 28 to secure the movable contact element 12 against pivotal movement around the axis of the rivet. With this arrangement the rivet and inter-engaging surfaces 38 and 39 on the body and projection 34 cooperate to lock the movable contact in its proper position, so that proper orientation of the movable contact is maintained even if substantial loads are Iapplied to the terminal 21.

A similar arrangement is provided to insure precise 1ocation of the fixed contact element 11. In this instance the fixed contact element 11 is provided with opposed edges 41 and 42 which closely iit opposed wall surfaces 43 and 44, respectively, formed in the body 10` as best illustrated in FIGURE 4. The opposed surfaces 38 and 39 which position the movable contact 12 and the opposed surfaces 43 and `44 which position the fixed contact 11 are all spaced a substantial distance from the rivet 28. Therefore, the manufacturing tolerances required, for a given accuracy of positioning of the contacts, are not as sm-all as would be required if the locating surfaces were closer to the rivet. The fixed contact element 11 is insulated from Ithe rivet 28 by a shallow, tubular extension 46 formed on the body 10 to closely tit into an opening 47 in the mounting portion 13. The rivet 28 extends up through this tubular extension `46 so the rivet is insulated from the mounting portion 13 while securely positioning the 'fixed contact element 11 in position. The extension 34 of the substantially rigid part 18 is bent at its end toward the insulating member 24. Therefore, the edge 35 at the end of the rigid part 18 presses against the insulating member 26 to insure that the outer end of the insulating member is properly seated in the step recess 40 in the body 10.

Accurate positioning of the contact button 17 in a vertical direction, as viewed in FIGURES 3 and 4, is provlded by a locating projection 51 molded int@ lh@ body 10 directly below the contact button 17. The tixed contact element 11 is formed so that it is bent slightly from its unstressed condition by its engagement with the locating projection 51 when the switch is `assembled. With this arrangement accuracy of positioning of the contact button 17 is achieved `without extremely close tolerances in the manufacture of the contact 11, and the contact button 17 does not move when the switch operates.

In FIGURE 4a a modilied structure is illustrated to position the fixed contact. Similar reference numerals are used to describe similar elements, since the principal structure is substantially identical to the first embodiment of FIGURES 1 through 4. However, primes are added to indicate reference to the embodiment of FIGURE 4a. The body 10 is provided with a recess 52 proportioned to receive a tongue 53 on the iixed contact element 11. The lateral or opposite walls of the recess 52 are proportioned to closely lit the side Walls or edges of the tongue 53 and cooperate with the single rivet to provide lateral support and accurate lateral positioning of the fixed contact button 17. The accurate vertical positioning of the 4fixed contact button 17 is provided by the engagement of the under side of the tongue 53 with the bottom wall of the recess 52'. Here again, during mounting of the lixed contact element 11 it is bent slightly from its unstressed condition by the engagement of the lower side of the tongue 53 withrthe bottom of the recess 52' to insure proper contact and support.

Referring again to FIGURES l through 5. The flexible switching element 12 is operated by a plunger 54 which extends through a guide opening 56 in the body 10 and a clearance opening 57 in the lixed contact 11. The upper end 58 of the plunger 54 is formed with a spherical surface adapted to engage the under side of the movable contact 12 and deflect it upwardly to lift the second contact button 24 away from the rst button 17 when the switch is to be opened. The lower end of the plunger 54 is also formed with a spherical end 59 adapted to engage a snap disc 61. In the illustrated embodiment the snap disc 61 is formed of a bimetallic material and is shaped so that it assumes a downwardly arched position, as illustrated in FIGURE 3, when it is at temperatures above a predetermined upper temperature and snaps through to an upwardly arched position, as illustrated in phantom at 61a, when the disc is at temperatures below a predetermined lower temperature.

With such an arrangement the switch is closed when the disc is in the position of FIGURE 3. This occurs when the disc is at a temperature above an upper predetermined temperature. The flexible part is deflected from its unstressed condition and presses the contact button 24 against the contact button 12 with sutiicient pressure to assure a good electrical connection. The switch is opened when the disc snaps to the phantom position of 61a. This occurs when the disc is at a temperature below a lower predetermined temperature. The movement of the disc 61 to the phantom position operates to push the plunger 54 and the flexible contact 12 causing the movable contact button 24 to move out of engagement with the fixed contact button 17.

If it is desired to provide the opposite switching action the disc 61 is assembled in an inverted position. When this is done the switch closes as temperature decreases and opens as temperature increases. It should also be understood that the switching device may utilize snap acting discs of other known types. For example, the switch may be operated by a snap disc actuated by changes in fluid under pressure.

The snap disc 61 is mounted at its periphery 62 between opposed surfaces 63 and 64 formed on the body 10- and a cup-shaped cover member 66, respectively. Lateral sup port for the disc is provided by an inner cylindrical wall 67 on the cover member 66. Preferably, the cover member .66 is formed of a metal stamping. Accurate radial positionmg of the cover member 66 is provided by engagement between an inner cylindrical wall 67 on the cover member and a mating external cylinder wall 68 on the body 10. Accurate axial positioning of the cover is provided by engagement between a radial surface 69 on the cover member 66 with a radial mating surface 71 on the body 10. The cover member 66 is secured in position by four symmetrically located projections 72 (best illustrated in FIGURES l and 2) which are formed by radially deforming the cover into mating grooves 73 in the body. The grooves 73 extend to a lower end 74 so that the deformed projections 72 engage the end surface and hold the radial surfaces 69 and 71 in engagement. The central portion of the cover member 66 radially inward from the surface 64 is displaced downwardly at 76 to provide space for the disc 61 when it is in the downwardly arched position of FIGURE 3. If desired, the end wall at 76 can be removed to directly expose the disc 61.

The two opposed surfaces 63 and 64 are spaced from each other a suficient distance so that the periphery 62 of the snap disc 61 is not pinched, but is loosely retained in position. With this arrangement the snap action occurs at temperatures determined by the structure of the disc and the operating temperature is not affected by the mounting of the disc in the body.

FIGURES 6 and 7 illustrate a second embodiment for mounting the cover member on the body. In this embodiment similar reference numerals are used to designate similar parts, but a prime is again added to indicatev that the modified or second embodiment is referred to. The body 10 is formed with a cylindrical wall 68 which extends from the end surface 63 to an oppositely facing surface 74. The cover member 66 is formed with an inner cylindrical surface 67 closely fitting the outer cylindrical surface 68' to radially locate the cover member.

The axial positioning of the cover member is provided by an engagement between the top of an annular rim 81' with a downwardly facing radial surface 82. This downwardly facing surface 82 is formed on the underside of the projecting portions 83 of the body 10. In order to securely position the cover member 66 on the body 10' the rim 81' is staked at 84 over the surface 74 in four symmetrically located positions as illustrated in FIGURE 6. The staking serves to hold the upper edge of the bead 31 in engagement with the surface 82 and provides the precise axial location of the cover member relative to the body. Here again, the various elements are proportioned so that a loose fit is provided between the surfaces 63' and 64 and the periphery 62 of the disc 61' so that operating temperature accuracy is not adversely affected. In this embodiment the staking in the four locations 84' can be achieved by utilizing a single appropriately shaped tool which is axially pressed down against the rim 81 to simultaneously stake all four locations 84'.

In the illustrated embodiments of this invention a single rivet 28 is the only fastening means required to securely mount the two contacts 11 and 12 and the cover insulating member 26 on the body 10. The contact members 11 and 12 are provided with opposed edges spaced from the rivet 28 which cooperate with adjacent surfaces in the body to insure accurate location of the contact members even though a single fastener is used. The insulating member 26 performs dual functions of separating the contact elements 11 and 12 and also closing the switch cavity 27. Consequently, the number of parts required for the switching structure is minimized. The fixed contact element is defiected from its unstressed condition by engagement with a mating surface on the body at a point adjacent to the fixed contact button to insure accurate location of the contact button.

Accuracy of operation, without requiring extremely close manufacturing control, is also improved by locating the weld points 23 on the side of the rivet 28 remote from the contact portion 30. The spring rate of the movable contact 30 is determined by the physical properties of the exible part and the effective length of the spring. When the mounting portion 29 of the flexible part is in engagement with the rigid part 18 at the line of the bend 86 the bend line acts as a pvot point and the spring rate of one movable contact is substantially the same as the spring rate of similar movable contact in similar thermostats. It is, therefore, desirable to insure a proper engagement at the line 86.

If the welds 23 were located Ibetween the rivet 28 and the pivot line 86, extremely close production control would be required to insure that the welding did not produce a small spacing between the flexible part and rigid part at 86. However, by locating the welds 23 at the illustrated location such accurate welding control need not be provided. With this arrangement slight spacing can exist adjacent to the weld without causing a space at 86, since the rivet presses the flexible part against the rigid part and contact along the line 86 is insured.

In the illustrated embodiments the accuracy and reliability of the thermostatic switching device is properly achieved with a reduced number of parts and a reduced number of assembly operations. Consequently, an accurate, reliable, and low cost thermostatic device is provided.

Although preferred embodiments of this invention are illustrated, it is to be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention.

I claim:

1. A thermostat comprising a body formed with a switch cavity having an opening, a first contact having a mounting portion and a Contact portion projecting into said cavity, an insulating member extending across and substantially closing said opening, said insulating member overlying said mounting portion of said first contact, a second contact having a mounting portion overlying said mounting portion of said first contact and separated therefrom by said insulating member, said second contact including a contact portion projecting into said cavity and overlying said contact portion of said first contact, a fastener extending through both of said mounting portions and said insulating member mounting them on said body, said fastener being insulated from at least one of said mounting portions one of said contact portions being laterally supported against lateral movement by opposed walls of said cavity, and temperature responsive means operable to move the other of said contact portions into and out of contact with said one contact portion.

2. A thermostat as set forth in claim 1 wherein said opposed walls of said cavity are substantially spaced from said fastener.

3. A thermostat as set forth in claim 1 wherein said one contact portion is deflected from its unstressed condition toward said other contact portion by engagement with a locating surface on said body.

4. A thermostat as set forth in claim 3 wherein said body is formed with a recess adjacent to the end of said one contact portion to provide said opposed walls and said locating surface, and said one contact portion is formed with an end proportioned to closely fit said recess.

5. A thermostat as set forth in claim 1 wherein both of said contacts are supported against lateral movement by abutting wall surfaces on said body spaced from said fastener.

6. A thermostat as set forth in claim l1 wherein said second contact includes a flexible element and a substantially rigid element electrically connected to said flexible element, said flexible element providing said contact portion of said second contact, said flexible element projecting into said cavity through an aperture in said insulating member, and said substantially rigid element extending over said aperture and cooperating with said insulating member to close said cavity.

7. A thermostat as set forth in claim 6 wherein said substantially rigid element is formed with an edge pressing against said insulating member on the side of said aperture remote from said fastener, said edge tending to press the end of said insulating member remote from said fastener into tight engagement with said body.

8. A thermostat as set forth in claim 6 wherein said body is formed with a step recess extending substantially around said opening, said-insulating member closely f1tting said step recess, and the portion of said substantially rigid element extending over said aperture closely itting the side walls of said recess to cooperate with said fastener to limit lateral movement of said contact portion of said second contact.

9. A thermostat as set forth in claim 1 wherein said temperature responsive means includes a snap disc, and operator means operable to move said other contact portion in response to snapping of said disc.

10. A thermostat as set forth in claim 9 wherein said snap disc is formedof bimetallic material.

11. A thermostat as set forth in claim 9 wherein sai snap disc is mounted on said body by a cup-shaped cover member, said cover member and body each being formed with closely fitting opposed cylindrical surfaces cooperating to radially locate said cover member relative to said body, and opposed radial surfaces on each of said body and cover member, the opposed radial surfaces on said body engaging corresponding opposed radial surfaces on said cover member to axially locate said cover member with respect to said body, at leastone of said opposed radial surfaces of `said cover member being provided by a radial deformation in the wall of said cover member.

12. A thermostat asr set lforth in claim 11 wherein said body and cover member cooperate to provide snap-.disc retaining surfaces including a cylindrical surface around the periphery of said snap-disc to radially locate said disc, and spaced opposed radial surfaces to axially position the periphery of said snap-disc.

13. A thermostat as set forth in claim 11 wherein a plurality of peripherally spaced, radial deformations are formed in a cylindrical wall of said cover member.

14. A thermostat as set forth in claim 13 wherein said body is formed with a plurality of peripherally spaced recesses, and said cover member is radially deformed into said recesses to form said radial deformations.

15. A thermostat as set forth in claim 11 wherein said cover member is formed with an axially extending annular rim at one end, and said rim is radially deformed to provide said radial deformation at spaced locations around said rim, said radial deformation being formed by axially applied forces.

16. A thermostat comprising a body assembly formed with a switch cavity, a fixed contact on said body having a contact portion in said cavity, a movable contact including a exible element and a substantially rigid element, said flexible element including a mounting portion extending along said rigid element in engagement therewith and a movable contact portion `free of said rigid element joined to said mounting portion along a line, a fastener extending through said rigid element and said mounting portion of said flexible element pressing them together and mounting said movable Contact on said body, and a weld on the side of said fastener remote from said line connecting said rigid element and said mounting portion.

References Cited UNITED STATES PATENTS 7/1957 Rosenberg et al. 337--348 1/ 1965 Ruckriegel et al. 337--348 U.S. Cl. X.R. 337-348, 354 

